The present invention relates to apparatus for treating scrap material and more particularly to the construction of a hammer mill designed to comminute such scrap material. The hammer mill to which the present invention relates is of a type consisting of a housing having a material inlet and a material outlet, with the outlet being covered by a classifying grate. A rotor is rotatably supported in the housing with hammer means being spaced peripherally about the rotor to effect comminuting of material when the rotor is rotated. The invention relates to a specific configuration of a hammer mill of the type described.
Hammer mills of this type have been known in the prior art, for example in U.S. Pat. No. 3,482,788. In this prior art device, the material outlet in the housing is covered with a classifying grate which is located at the upper end of a gathering box or discharge chute which extends vertically from the periphery of a rotating rotor which thrusts comminuted material upwardly toward the housing outlet by centrifugal force of the rotor. The openings of the classifying grate at the material outlet allow the material to be emitted therefrom when a particular size compatible with the openings in the grate has been achieved. The grate openings are formed with comparatively large cross-sectional areas in order to prevent clogging of the grate by coarse but relatively light comminuted material.
In the operation of the device disclosed in U.S. Pat. No. 3,482,778, a large portion of the material which is severed from an initial piece of material introduced through the apparatus inlet is thrown or thrust outwardly through the classifying grate without obstruction. A smaller portion of the material is first deflected at or by the grate bars and/or the walls of the gathering box or chute. This portion ultimately falls back on to the rotor to be further comminuted and/or condensed by operation of the hammer mill.
However, experience has shown that apparatus of this type is not well suited for all scrap material. Particularly, when it is desired to comminute scrap material which may, for example, be derived from automobile bodies, it is advantageous to avoid overly rapid discharge of the material. It becomes at times desirable and more economic to effect greater condensation or comminution of the scrap material in order to achieve as small a size as possible for each piece of the scrap material and to thereby achieve a higher bulk density. However, in known hammer mills of the type to which the present invention relates, extension of the time over which the material may be worked within the mill by the rotor in order to effect a greater degree of condensation occurs only to a relatively small degree. For example, in the apparatus of U.S. Pat. No. 3,482,788, the gathering box essentially serves for angular alignment of the scrap pieces so that they may be guided through the classifying grate at the outlet. Additionally, it appears that in known apparatus of this type, the material to be comminuted is dragged or pulled by the hammers of the hammer rotor along the housing bottom between the material inlet and the material outlet, thus causing wear of the housing bottom without performance of a comminuting and/or deforming effect upon the material being treated in the hammer mill.
In the passage of scrap material through various sections of a hammer mill, a significant amount of energy, primarily in the form of kinetic energy expended during passage of the material through its path of travel, may be expended without useful purpose. For example, in the device of U.S. Pat. No. 3,482,788, kinetic energy in the area of the gathering box or in the vicinity of the housing bottom may be expended in the form of friction losses. Thus, as the material travels from material inlet to material outlet through the hammer mill housing, substantial energy which could otherwise be used for the intended purpose of material deformation or comminution, remains unused and is wasted.
The present invention is drawn toward the task of creating a hammer mill of the type discussed above which will better utilize available energy in order to achieve a more uniform size of the material which is to be comminuted and to simultaneously reduce wear in the apparatus. The invention is, thus, directed toward the task of effecting desired condensing and/or comminuting a waste material introduced into a hammer mill with greater effectiveness and improved economy.